1. Field of the Invention
The present invention relates to a wafer susceptor, and more particularly, to a wafer susceptor capable of functioning as the RF electrode and the heater.
2. Description of the Related Art
A plasma enhanced chemical vapor deposition (PECVD) is widely used as one of processes for manufacturing a semiconductor device. Unlike a typical chemical vapor deposition (CVD), since the PECVD proceeds to a process in a state that a process gas is activated using a plasma, it has several advantages, for example, that the process can be performed at a lower temperature than the conventional CVD.
FIG. 1 is a schematic view of a typical PECVD apparatus. Referring to FIG. 1, a susceptor 70 on which a wafer 25 is disposed is mounted within a reaction chamber 10 and an upper RF electrode 30 is mounted on an upper portion of the reaction chamber 10.
Typically, because the PECVD apparatus does not have a dual RF source, a lower electrode (i.e., the susceptor 70) is grounded. In addition, the upper electrode is a plate-shaped electrode or a dome-shaped electrode and an RF power is applied to the upper electrode. In some cases, in order to improve a characteristic of film quality, the RF power may be applied to the lower electrode (i.e., the susceptor).
If the RF power is applied to the upper RF electrode 30, a plasma is generated within the reaction chamber 10. If the plasma is generated, positive ions existing within the plasma are attracted toward the wafer 25 due to a self-bias, so that a thin film is deposited on the wafer 25. Typically, the susceptor is grounded. In some cases, however, in order to maximize this effect, the lower RF electrode 22 is mounted within the susceptor 70 and the RF power is also applied to the lower RF electrode 22. Further, a stress level of the thin film deposited on the wafer 25 can be controlled by applying the RF power to the lower RF electrode 22. Furthermore, it is possible to protect patterns formed on the wafer from being damaged due to the plasma. This is because the RF power removes charges which are accumulated between the patterns.
Meanwhile, in order to deposit a high-density film on the wafer 25, it is necessary to heat the wafer at 500xc2x0 C. or higher. Typically, a heater (not shown) is mounted within the susceptor 70 for the purpose of the heating process.
If the RF power is applied to the lower RF electrode, however, the heater is affected by an RF noise so that a reliable thin film is not formed. This is because an efficiency of the plasma may be degraded and a system for controlling a temperature of the heater may be also affected.
Therefore, the present invention has been devised to solve the above problems, and it is an object of the present invention to provide a wafer susceptor functioning as the RF electrode and the heater, thereby capable of minimizing an influence of RF noise on the heater.
To achieve the aforementioned object of the present invention, there is provided a wafer susceptor comprising: a ceramic body; an RF electrode mounted within the ceramic body; a heater mounted within the ceramic body and spaced apart from the RF electrode by a predetermined distance to be disposed below the RF electrode; and an RF shield of a metal material, the RF shield being electrically grounded and mounted within the ceramic body, the RF shield being disposed between the RF electrode and the heater without being in contact with either the heater or the RF electrode.
At this time, the RF shield can be formed using a metal plate, a net or a thin film coated on the ceramic body.